The present invention relates to a deflection yoke used with a color cathode ray tube for generating a plurality of in-line arranged electron beams and a color cathode ray tube using the same and, particularly, to a deflection yoke equipped with a convergence correction device and a color cathode ray tube using the same.
An example of a conventional deflection yoke having a convergence correction device is disclosed in, for example, Japanese Patent Application Laid-open No. H3-247093. In the deflection yoke disclosed, a set of diodes are connected in opposite directions to an upper portion correcting coil and a lower portion correcting coil, respectively, and a second impedance element is connected between junctions of the diodes and the respective correcting coils associated therewith. By connecting a first impedance element in parallel to the above mentioned circuit, both the non-linear coma aberration and the YH mis-convergence are corrected simultaneously.
In the disclosed conventional technique, however, the diodes are non-conductive during a period where an amount of vertical deflection is small and a current flowing through the first impedance element is small. Therefore, it is impossible to correct the YH mis-convergence while maintaining the linearity of the correction of coma aberration.
Further, in the disclosed technique, there is no measure taken to meet the problem of change of the amounts of correction of the coma aberration and the YH mis-convergence with change of temperature due to the temperature characteristics of forward voltage of the diodes.
In addition thereto, the disclosed prior art can not correct the mis-convergence in the shape of crossed vertical lines.
Further, in the disclosed prior art, it is impossible to regulate the mis-convergence of the vertical lines in an upper half and a lower half of a screen of the cathode ray tube, individually.
Japanese Patent Application Laid-open Nos. H3-82290 and H4-286841 disclose techniques similar to that disclosed in Japanese Patent Application Laid-open No. H3-247093.
An object of the present invention is to provide a deflection yoke with which it is possible to correct the YH mis-convergence while maintaining the linearity of correction of the coma aberration, to reduce a change of correction amount of the coma aberration and the YH mis-convergence with change of temperature and to correct the mis-convergence in the form of crossed vertical lines.
Another object of the present invention is to provide a deflection yoke with which the mis-convergence of the vertical lines can be regulated for the upper half and the lower half of the screen individually.